|M.Sc Student||Poem-Kalogerakis Eilon|
|Subject||Many Carrier Energy Levels in Semiconductor Quantum Dots,|
and Selection Rules for Optical
Transitions between Them
|Department||Department of Physics||Supervisor||Professor David Gershoni|
In this work we present experimental and theoretical study of the polarized photoluminescence spectrum of single semiconductor quantum dots in various charge states. We compare our high resolution polarization sensitive spectral measurements with a new many-carrier theoretical model which was developed for this purpose. The model considers both the isotropic and anisotropic exchange interactions, between all participating electron-hole pairs. With this addition, we calculate both the energies and polarizations of all optical transitions between collective, quantum dot confined charge carriers’ states. We succeed in identifying most of the measured spectral lines. In particular the lines resulting from positively and negatively charged biexcitons and doubly charged excitons and biexcitons.
In addition, the electron-hole exchange interaction energies were deduced from the measurements. In particular, the energies in cases where one of the carriers is in the first single-carrier level and the other is in the second level, were found to be opposite in sign to the interaction energy where both carriers are in the first level.
Using the model, the influence of external electric and magnetic fields on the spectrum was calculated and compared with electro- and magneto-photoluminescence spectroscopy experiments.
For electric field, the calculated and measured Stark shifts are comparable.
For magnetic field, while the calculation for a cylindrically symmetrical model quantum dot well agrees with the measured diamagnetic shifts, deviation from this symmetry results in disagreement. The calculations show a shift towards lower emission energies for some of the spectral lines. Similar shifts have not been observed in the measurements.